<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script src="../lib/jquery-3.2.1.js"></script>
</head>
<body>
    <div style="display:block;">hello world</div>
    <button>toggle</button>
    <script>
        $("button").click(function(){
            var d = $("div").css("display")
            if(d=="block"){
                $("div").css("display","none")
            }else{
                $("div").css("display","block")
            }
        })
    </script>
</body>
</html>